Disease-inflicted damages on rice production are significant. In the field of agriculture, while agrochemicals are used for disease control, due to concerns regarding the cost of agrochemicals and their effects on the human body and the environment, rice cultivation with no or little use of agrochemicals is desirable. In particular, methods utilizing genes are thought to be effective, and in recent years, disease-resistance genes have been isolated from Arabidopsis thaliana—a model plant. However, since screening for disease-resistance genes has been carried out mainly using loss-of-function as the indicator, many important genes may have been overlooked.
Meanwhile, in the disease response of Arabidopsis thaliana, there is a signal transduction pathway in which salicylic acid (SA) functions as a signal molecule, and this molecular mechanism is being studied in detail. When a pathogen infects Arabidopsis thaliana, the intracellular SA concentration increases, causing induction of disease response reactions, which include changes in expression of a large number of genes including the PR genes, which are regulated downstream of SA in the signal transduction pathway. Furthermore, external treatment of SA or its derivative INA (2,6-dichloroisonicotinic acid) causes activation of the SA signal transduction system and induction of expression of the downstream-regulated disease-resistance genes and the PR genes.
In the SA signal transduction system, the NPR1 protein plays an important role (Non-Patent Document 2). It is known that in the npr1mutant of Arabidopsis thaliana, induction of expression of the disease-resistance genes and the PR genes by SA or INA is not observed, and the mutant cannot also be grown on a medium containing SA. However, when it comes to rice, findings relating to the SA signal transduction pathway and signal transduction factors involved in this pathway are extremely limited.
Prior art documents of the present invention are shown below.    [Non-Patent Document 1] Becker, D et al., (1990) Nucleic Acid Res., 18(1): 203.    [Non-Patent Document 2] Cao, H et al (1997) Cell 88:57-63.    [Non-Patent Document 3] Ichikawa, T et al., (2006) Plant J. 48: 974-985.    [Non-Patent Document 4] Kikuchi, S et al., (2003) Science 301: 376-379.    [Non-Patent Document 5] Mori, M et al., (2007) Plant Mol. Biol., 63:847-860.    [Non-Patent Document 6] Nakamura, H et al., (2007) Plant Mol Biol. 65:357-371.    [Non-Patent Document 7] Taji, T et al., (2002) Plant J., 29(4): 417-426.    [Non-Patent Document 8] Toki, S et al., (2006) Plant J. 47:969-76.